Lead levels in the water are dropping in Flint, Michigan, marking "the beginning of the end of the public health disaster," according to the Virginia Tech University researchers who exposed the lead problem in that troubled northern U.S. city a year ago. But residents still should continue to drink only filtered tap water or bottled water while the system heals itself, lead researcher Marc Edwards told a news conference Thursday. In the most recent round of testing in July, 45 percent of homes did not have detectable levels of lead, compared to only 9 percent of homes in August 2015. "Flint water now looks like it's entering a range that is considered normal for U.S. cities," Edwards said. "Things are dramatically better now.'' U.S. federal health officials found that young children in Flint had significantly higher levels of dangerous lead in their blood after the city switched its water supply from the Detroit water system to the Flint River as a cost-cutting measure. The city switched its water supply in 2014 without ensuring that water from the Flint River had been treated with anti-corrosive agents, as required by law. It corroded the city's old water mains, turning drinking water brown due to iron contamination, and also leached lead from smaller pipes that carried water into homes. In all, nearly 100,000 people were affected by the contaminated water. Lead in water supplies can cause profound and permanent health problems, particularly in children whose brains and nervous systems are still developing.